Multisystem Inflammatory Syndrome in Children — Initial Therapy and Outcomes

DISEASE SURVEILLANCE

The Overcoming COVID-19 surveillance registry was funded by the Centers for Disease Control and Prevention (CDC) to conduct surveillance of Covid-19–related severe complications, including MIS-C as defined according to CDC criteria,¹⁸ in children and adolescents hospitalized in the United States and to collect detailed data. Patients with MIS-C were identified at each site by intensive care unit (ICU) and subspecialty clinicians and through mandated public health reporting. Trained staff at participating facilities abstracted medical records onto a standard form and entered data into a Web-based secure electronic database (Research Electronic Data Capture [REDCap], Vanderbilt University). Data collected included the demographic characteristics of the patients, underlying medical conditions, signs and symptoms at presentation, clinical course, laboratory test results, diagnostic studies, treatments, complications, and outcomes. The surveillance protocol, which is available with the full text of this article at NEJM.org, was approved by the central institutional review board at Boston Children’s Hospital, with a waiver of informed consent. It was also reviewed by the CDC, and all activities were conducted in accordance with applicable federal law and CDC policy. The last two authors vouch for the accuracy and completeness of the data and for the fidelity of the study to the protocol.

CASE DEFINITION

Cases were adjudicated by the principal investigators at each site and at the central coordinating center. The case definition of MIS-C included six criteria¹⁸: serious illness leading to hospitalization, an age of less than 21 years, fever (body temperature, >38.0°C) or report of subjective fever lasting at least 24 hours, laboratory evidence of inflammation, multisystem organ involvement (i.e., involving at least two organ systems), and laboratory-confirmed SARS-CoV-2 infection (positive SARS-CoV-2 real-time reverse-transcriptase–polymerase-chain-reaction [RT-PCR] or antibody test during hospitalization) or an epidemiologic link to a person with suspected or confirmed Covid-19 within 4 weeks before the onset of MIS-C symptoms. Owing to a lack of SARS-CoV-2 testing in the spring of 2020, cases reported between March 15 and May 31 as suspected or confirmed MIS-C cases that were epidemiologically linked to a Covid-19 exposure were included without the requirement of a positive SARS-CoV-2 test; positive testing was required after May 31.

IMMUNOMODULATORY TREATMENTS

Two approaches were used to categorize patients with MIS-C. First, we categorized patients according to the immunomodulatory treatments they received at any time during their hospital course: IVIG only; IVIG and glucocorticoids; IVIG, glucocorticoids, and a biologic agent; or other treatments (glucocorticoids only, a biologic only, glucocorticoids and a biologic, or IVIG and a biologic). Glucocorticoids included methylprednisolone, prednisolone, and dexamethasone. Biologics included an interleukin-1–receptor antagonist (anakinra), tumor necrosis factor α inhibitors (infliximab and etanercept), and an interleukin-6–receptor antagonist (tocilizumab).

Second, we classified patients according to which of two commonly used¹⁹ treatments they received on day 0, which was termed their “initial treatment”: IVIG plus glucocorticoids or IVIG alone. Day 0 was defined as the first day a patient received any immunomodulatory treatment (which was not necessarily the first day of hospitalization). Days 1 and 2 were the first and second calendar days after day 0. Available data included the calendar day for all the treatments but not the calendar time. Glucocorticoids (in patients not already receiving glucocorticoids on day 0), biologics, and second doses of IVIG administered on or after day 1 were considered “adjunctive” treatment. Patients who received a biologic on day 0 were excluded because of small sample size and the use of multiple types of biologics with varying cytokine targets.

OUTCOMES

We report the following outcomes for patients who received any immunomodulatory treatment during hospitalization: admission to the ICU, receipt of supplemental oxygen, receipt of mechanical ventilatory support, use of vasopressor agents, receipt of extracorporeal membrane oxygenation, hospital length of stay, coronary-artery aneurysms, and death. Coronary-artery aneurysms were defined as a z score of at least 2.5 for the left anterior descending coronary artery or the right coronary artery (or both) on echocardiography.⁷

To assess the potential effectiveness of initial treatment with IVIG plus glucocorticoids, as compared with IVIG alone, we prespecified a primary outcome of cardiovascular dysfunction on or after day 2 through the time of discharge, which was based on a composite of left ventricular dysfunction (as defined by a left ventricular ejection fraction [LVEF] of <55% on echocardiography) or shock that resulted in the use of vasopressors. This composite cardiovascular outcome was chosen because, in this MIS-C cohort,⁶ low LVEF did not always result in the use of vasopressors and distributive shock was not always associated with low LVEF; however, either finding would influence therapy decisions. Outcomes were measured on or after day 2 to allow for a clinical response after initial treatments.⁶ Secondary outcomes were the individual components of the primary outcome, the receipt of adjunctive immunomodulatory treatment on or after day 1, persistent or recurrent fever (body temperature, >38.0°C) on or after day 2, and length of stay in the ICU (counted starting from the day of initial treatment [day 0]). Data on treatment-related adverse events were not collected as part of the registry.

STATISTICAL ANALYSIS

Continuous variables were expressed as medians and interquartile ranges or ranges, and categorical variables were expressed as counts and percentages. To assess the associations between initial treatment with IVIG plus glucocorticoids, or with IVIG alone, and the primary and secondary outcomes, we used propensity-score matching and an inverse-probability-weighted analysis, with adjustment for confounding factors that might have influenced treatment choices.²⁰

We modeled the probability of treatment using logistic regression and used the estimated probability as a propensity score. We included relevant baseline variables that might have affected treatment decisions. These included demographic characteristics (age, race or ethnic group, and sex), preexisting conditions, commonly measured laboratory markers of inflammation on the day of admission (neutrophil-to-lymphocyte ratio, C-reactive protein level, and platelet count), and clinical observations at admission (Kawasaki’s disease–like features [as defined by American Heart Association guidelines⁷], severe cardiovascular or respiratory involvement, vasopressor use, receipt of mechanical ventilation, pulmonary infiltrates on radiographic imaging, and admission to the ICU). Variables were selected on the basis of clinical experience,^1,21,22 review of paired correlations, and the success of balancing distributions of treatment groups. We excluded patients who had missing laboratory test results, and we performed a complete-case analysis after covariates were selected.

In the propensity-score–matched analysis, we used “greedy nearest-neighbor” matching without replacement. Here, the matching algorithm first selected a patient who had received IVIG plus glucocorticoids and then selected a patient who had received IVIG alone who had a linear propensity score that was closest to that of the first selected patient. We used a 1:1 ratio within a caliper width of 0.2 of the standard deviation of the logit of the propensity score. Risk ratios and 95% confidence intervals were calculated to quantify the association between the treatment and outcome with the use of log-binomial regression models. We adjusted for treatment site in the propensity-score–matched analysis using generalized estimating equations clustered according to treatment site with an exchangeable correlation structure. We then evaluated the potential effectiveness of treatment on the primary and secondary outcomes using an inverse-probability-weighted analysis to maintain all members of the treatment-comparison cohort by assigning each patient a weight that was based on the propensity score. We used the matching package from R software, version 4.0.2, for the propensity-score–matched analysis and SAS software, version 9.4, for the inverse-probability-weighted analysis.

PATIENT CHARACTERISTICS OF THE COHORT

Patients with MIS-C Treated with Immunomodulatory Therapies in the Overcoming COVID-19 Surveillance Registry.Table 1.

Of 596 patients with MIS-C who were admitted to 58 participating hospitals between March 15 and October 31, 2020, a total of 518 (87%) received at least one immunomodulatory treatment during hospitalization (Figure 1 and Table 1). The median age of the patients was 8.7 years (interquartile range, 4.9 to 12.8; range, 0 to 20.9), 217 patients (42%) were female, 183 (35%) were Black non-Hispanic, 174 (34%) were Hispanic or Latino, and 390 (75%) had been previously healthy (i.e., they had no preexisting conditions and had not been receiving any prescription medications). More than half the patients (286 [55%]) had involvement of five or more organ systems, 196 (38%) met complete or incomplete criteria for Kawasaki’s disease, 385 (74%) received care in the ICU, and 9 (2%) ultimately died (Table S1 in the Supplementary Appendix, available at NEJM.org). The patients who received IVIG alone were somewhat younger than those in other treatment categories, and half these patients had Kawasaki’s disease–like features.

Among the 518 patients who were treated with immunomodulatory therapies during hospitalization between day 0 and discharge, 89 (17%) received IVIG only; 241 (47%) received IVIG and glucocorticoids; 107 (21%) received IVIG, glucocorticoids, and a biologic; and 81 (16%) received other treatments, including glucocorticoids only, a biologic only, glucocorticoids and a biologic, or IVIG and a biologic (Table 1). Methylprednisolone was the most common glucocorticoid prescribed (in 353 patients [68%]); it was administered at a dose of 2 mg per kilogram of body weight per day in 284 of these patients (80%) and in pulse doses of 10 to 30 mg per kilogram per day in 69 of these patients (20%) (Table S2). The most common initial treatments given on day 0 were IVIG alone (in 192 of 518 patients [37%]) and IVIG plus glucocorticoids (in 157 of 518 patients [30%]). Only 34 patients received a biologic on day 0.

CLINICAL OUTCOMES ASSOCIATED WITH TREATMENTS GIVEN DURING HOSPITALIZATION

Overall, in patients who received immunomodulatory treatments at any time during hospitalization, the severity of illness was high with marked treatment heterogeneity; patient characteristics and clinical outcomes differed according to the immunomodulatory treatment combinations received (Table 1). Treatment patterns changed over time (Figure 2A). Immunomodulatory medications were administered early after hospitalization and in rapid succession; most treatments were given within 2 days after admission (Table S2). The 107 patients in the group that received IVIG, glucocorticoids, and biologic therapy during their hospitalization had the highest illness severity, as evidenced by multiple indicators of critical illness (Figure 2B). A total of 245 patients (47%) received vasopressors. Among the 501 patients (97%) for whom at least one echocardiogram was obtained during hospitalization, coronary-artery aneurysms were documented in 64 (13%) and 212 (42%) had left ventricular dysfunction during hospitalization.

CLINICAL OUTCOMES ASSOCIATED WITH INITIAL TREATMENT ON DAY 0

Patients who received initial treatment with IVIG plus glucocorticoids, as compared with IVIG alone, differed with respect to demographic and clinical characteristics at baseline, laboratory markers, and severity of illness (Table 2). Among the 349 patients treated with IVIG plus glucocorticoids or IVIG alone on day 0, a total of 206 could be matched according to the propensity score (in a 1:1 ratio of IVIG plus glucocorticoids to IVIG alone); the baseline characteristics were well balanced in the propensity-score–matched and inverse-probability-weighted samples (Figs. S1 through S3).

Among the patients in the propensity-score–matched sample who received IVIG alone, 74 (72%) received an adjunctive treatment; 60 patients (58%) received glucocorticoids, 29 (28%) received a second dose of IVIG, and 13 (13%) received a biologic. Among the patients who received IVIG plus glucocorticoids, 30 patients (29%) received a second dose of IVIG and 11 (11%) received a biologic (Table S3).

In the propensity-score–matched analysis, initial treatment with IVIG plus glucocorticoids was associated with a lower risk of the composite outcome of cardiovascular dysfunction on or after day 2 than IVIG alone (18 of 103 patients [17%] vs. 32 of 103 patients [31%]; risk ratio, 0.56; 95% confidence interval [CI], 0.34 to 0.94) (Figure 3). The risks of the components of the composite outcome were also lower among those who received IVIG plus glucocorticoids than among those who received IVIG alone; left ventricular dysfunction occurred in 8% and 17% of the patients, respectively (risk ratio, 0.46; 95% CI, 0.19 to 1.15), and shock resulting in vasopressor use occurred in 13% and 24% (risk ratio, 0.54; 95% CI, 0.29 to 1.00). Patients treated with IVIG plus glucocorticoids had a lower risk of receiving adjunctive treatment on or after day 1 than those who received IVIG alone (34% vs. 70%; risk ratio, 0.49; 95% CI, 0.36 to 0.65) but did not have a lower risk of fever on or after day 2 (31% vs. 40%; risk ratio, 0.78; 95% CI, 0.53 to 1.13) (Figure 3 and Table S3). Clustering according to treatment site showed similar results (risk ratio, 0.56; 95% CI, 0.35 to 0.90). Regression estimates for the propensity-score–matched analysis are provided in Table S4, and the results of an analysis that assessed potential unmeasured confounding are provided in Table S5. The median length of stay in the ICU did not differ significantly between the initial-treatment groups after propensity-score matching: 2 days in the group that received IVIG plus glucocorticoids and 3 days in the group that received IVIG alone.

The inverse-probability-weighted analysis confirmed the findings of the propensity-score–matched analysis (Figure 3). Initial therapy with IVIG plus glucocorticoids was associated with a lower risk of the composite outcome of cardiovascular dysfunction than IVIG alone (20% vs. 24%; risk ratio, 0.65; 95% CI, 0.48 to 0.89), as well as a lower risk of each of the components of the composite outcome; left ventricular dysfunction occurred in 8% and 15% of the patients, respectively (risk ratio, 0.58; 95% CI, 0.32 to 1.02), and shock resulting in vasopressor use occurred in 16% and 20% (risk ratio, 0.59; 95% CI, 0.40 to 0.85). Patients treated with IVIG plus glucocorticoids also had a lower risk of receiving adjunctive treatment on or after day 1 than those who received IVIG alone (39% vs. 65%; risk ratio, 0.53; 95% CI, 0.44 to 0.62), and a lower risk of fever on or after day 2 (31% vs. 43%; risk ratio, 0.70; 95% CI, 0.56 to 0.88).

Among U.S. children and adolescents hospitalized for MIS-C, a wide variety of immunomodulatory medications were administered early during hospitalization and often with the rapid addition of glucocorticoids, second doses of IVIG, or biologics in critically ill patients. After adjustment for clinical characteristics, including measures of illness severity, IVIG plus glucocorticoids was associated with a lower risk of cardiovascular dysfunction than IVIG alone on or after day 2 following initial treatment, with cardiovascular dysfunction assessed on the basis of a composite outcome of left ventricular dysfunction (as defined by an LVEF of <55%) or shock resulting in vasopressor use. Initial receipt of IVIG plus glucocorticoids was also associated with less use of adjunctive immunomodulatory treatments later in hospitalization, but the risks of persistent or recurrent fever and length of stay in the ICU were not clearly lower with initial treatment of IVIG plus glucocorticoids than with IVIG alone. Until published data that define best practices are available, these data provide clinicians with additional evidence to guide treatment for MIS-C.

Our study builds on earlier studies of MIS-C that also describe the use of glucocorticoids with IVIG^23-25; these studies suggested that outcomes may be improved with glucocorticoids, although rigorous adjustment for baseline disease severity was not made. Ouldali et al.²⁶ recently used a propensity-score–matched analysis in an MIS-C cohort in France to compare the effects of initial treatment with IVIG and glucocorticoids (32 children) with those of IVIG alone (64 children). They reported that initial treatment with IVIG and glucocorticoids resulted in a lower risk of fever (the primary outcome) than IVIG alone. Their findings also suggested a lower incidence of receipt of adjunctive treatments and a lower risk of cardiovascular dysfunction. In our larger U.S. cohort, we confirmed that cardiovascular function was better and the incidence of administration of adjunctive treatments was lower among patients who received initial treatment with IVIG plus glucocorticoids than among those who received initial treatment with IVIG alone. We did not identify a strong treatment effect on persistent or recurrent fever, possibly owing to a higher incidence of adjunctive treatments in the U.S. cohort, in which half the patients who were given initial treatment with IVIG alone received glucocorticoids in the subsequent days.

Our study has certain limitations. First, the use of propensity scoring is less likely than randomized trials to balance unmeasured confounders, but on the basis of a sensitivity analysis for unmeasured confounding (i.e., E-value analysis), the introduction of a moderate confounder, independent of the measured confounders we included, would have been needed to change the primary outcome result.²⁷ More severely ill patients could have been treated more aggressively, but such an approach would have biased the results toward worse rather than better outcomes in the group that received IVIG plus glucocorticoids. Second, our study did not assess criteria for initiating immunomodulatory treatment for MIS-C. Third, although we had a sufficient sample size to use propensity-score matching for initial treatment with IVIG plus glucocorticoids as compared with IVIG alone, the benefits of other initial treatment regimens could not be analyzed. It is possible that a higher incidence of adjunctive immunomodulatory treatments in the group that received IVIG alone is related to the relative ease of later adding glucocorticoids. However, we did not assess the effect of individual medications (e.g., glucocorticoids alone) in the adjunctive treatment analysis owing to the potential effect of multiple comparisons. Accordingly, we are unable to draw a causal inference regarding the discrete effect of glucocorticoids. Fourth, a lack of baseline echocardiographic data before initial treatment for some patients did not allow for efficient inclusion of baseline left ventricular function in the propensity-score–matched analysis, and echocardiography was not standardized. Lastly, although we report deaths, we did not collect data on adverse events that could have been related to treatment, such as gastrointestinal bleeding, hyperglycemia, or allergic reactions to IVIG, nor did we obtain information regarding the duration or adverse effects of tapering of glucocorticoids in an outpatient setting.

The ongoing transmission of SARS-CoV-2 and the emergence of variants of concern²⁸ may promote continued outbreaks of MIS-C in the United States and internationally. Additional evidence-based studies are needed to examine the generalizability of our findings across a broad range of geographic regions and practice settings.

In a propensity-score–matched analysis, we found that initial treatment with IVIG plus glucocorticoids for MIS-C was associated with a lower risk of serious short-term outcomes, including new or persistent cardiovascular dysfunction 2 or more days later, than initial treatment with IVIG alone.